Pump TDH Calculator

TDH formula: TDH = Static Head + Friction Losses + Velocity Head + Pressure Head — for example, a system with 15 m static head, 3 m friction loss, and negligible velocity/pressure head has a TDH of roughly 18 m. Total Dynamic Head is the single most important number when selecting a centrifugal pump for any application — water supply, irrigation, drainage, firefighting, or industrial process water. Pump manufacturers publish a head-versus-flow performance curve for every model, and TDH is the value you match against that curve at your required flow rate. Get TDH wrong and the pump will either deliver far less flow than expected once it fights real system resistance, or it will run oversized and inefficient off its best-efficiency point — accurate TDH calculation is treated as the starting point of any pump selection exercise across pump industry trade literature and Hydraulic Institute standards.

TDH is built from four components in this calculator. The static head is the net vertical lift between the water source and the discharge point. If the pump sits above the water level, it has to overcome a suction lift, which adds directly to the head the pump must supply. If instead the source is above the pump (flooded suction, common on tanks and sumps feeding a pump below them), that head actually assists the pump and is subtracted: Static Head = Discharge Head + Suction Lift or Static Head = Discharge Head − Suction Head (flooded).

The friction loss accounts for energy lost to resistance inside the pipework — pipe wall roughness, bends, valves, strainers, and fittings on both the suction and discharge runs. This loss grows roughly with the square of flow velocity, which is why oversizing a pipe by even one size can meaningfully cut friction head, a relationship captured by the classic Hazen-Williams and Darcy-Weisbach equations used industry-wide. In the field, friction loss is usually taken from pipe friction charts or pump-house hydraulic calculations for the pipe size, length, and fittings involved, then entered directly here.

The velocity head represents the kinetic energy of the moving fluid at the discharge point, calculated as hv = V² ÷ (2 × g), where V is flow velocity in m/s (from flow rate ÷ pipe cross-sectional area) and g is 9.81 m/s². Velocity head is usually small for typical pipe velocities of 1–3 m/s but is included here for completeness, consistent with the full energy-balance form of the pump head equation covered in standard fluid mechanics references such as Cengel & Cimbala's Fluid Mechanics: Fundamentals and Applications.

Finally, if the pump must discharge into a pressurized vessel, boiler, or pressurized irrigation line rather than simply to atmosphere, that required pressure head is added by converting the pressure rating to an equivalent head of water, using the standard conversion of 1 bar ≈ 10.2 m of water head. Adding all four terms gives the final TDH: TDH = Static Head + Total Friction Loss + Velocity Head + Pressure Head.

Once TDH and flow rate are known, the hydraulic power the pump must impart to the fluid is P(kW) = (Q × H × ρ × g) ÷ 3,600,000, with Q in m³/hr, H in metres, and ρ = 1000 kg/m³ for water. Dividing by the pump's overall efficiency gives the shaft power the driving motor must supply — this figure, along with TDH and flow, is what you hand to a pump supplier or use to size the driving motor.

As with any sizing calculator, treat the result as an engineering starting point. Site-specific pipe condition, actual fitting counts, water temperature, and elevation changes over the pump's service life all shift the real-world number, so always confirm final TDH against as-built pipe layouts and verify the selected pump's published curve before purchase and installation.